Made available in DSpace on 2015-03-05T14:01:20Z (GMT). No. of bitstreams: 0 Previous issue date: 25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O avanço tecnológico e o valor que as informações representam no mundo moderno conduzem a uma constante busca por cifradores mais velozes, seguros e adaptáveis à diversos ambientes. Enquanto a segurança se baseia no comportamento complicado dos algoritmos, a eficiência se baseia na simplicidade das operações matemáticas envolvidas. Os sistemas caóticos têm a propriedade de exibir comportamento complicado mesmo sendo definido de modo determinístico por funções algebricamente simples. Portanto, a proposta de algoritmos de cifração baseados em sistemas caóticos é um tema de ativa pesquisa. Este trabalho estuda a eficiência e a segurança de um dos mais completos cifradores caóticos. Com base nesse estudo, melhorias são propostas tanto quanto à sua eficiência quanto à sua segurança. Com isto, chega-se a uma versão otimizada, a qual é referida ao longo deste trabalho como cifrador caótico (CC). O cifrador resultante não possui as fraquezas dos algoritmos caóticos propostos até então. Além disso, comparações exper / The technological advance and value of information in the preset days lead to a constant search for more efficient, secure and adaptable ciphers. While de security is based on the complicated behavior of the algorithms, its efficiency is based on the simplicity of the mathematical operations involved. The chaotic systems are characterized by the property of showing complex behavior even being defined by simple algebraic mathematical expressions. Therefore, the proposal of ciphers based on chaotic dynamics has became an active research field. This work deals with the efficiency and security of one of the most complete chaotic cipher proposed so far. Based on this study, improvements are proposed for both efficiency and security. The final result is an optimized version, which is denominated chaotic cipher (CC) towards this work. This cipher does not suffer from the weaknesses of the chaotic ciphers proposed so far. Moreover, experimental comparisons shows that the CC performance is comparable with those of s

As the aviation industry expands, consuming oil reserves, generating carbon dioxide gas and adding to environmental concerns, there is an increasing need for drag reduction technology. The ability to maintain a laminar flow promises significant reductions in drag, with economic and environmental benefits. Whilst development of flow control technology has gained interest, few studies investigate the impacts that uncertainty, in flow properties, can have on flow stability. Inclusion of uncertainty, inherent in all physical systems, facilitates a more realistic analysis, and is therefore central to this research. To this end, we study the stability of stochastic shear flows, and adopt a framework based upon the Wiener Chaos expansion for efficient numerical computations. We explore the stability of stochastic Poiseuille, Couette and Blasius boundary layer type base flows, presenting stochastic results for both the modal and non modal problem, contrasting with the deterministic case and identifying the responsible flow characteristics. From a numerical perspective we show that the Wiener Chaos expansion offers a highly efficient framework for the study of relatively low dimensional stochastic flow problems, whilst Monte Carlo methods remain superior in higher dimensions. Further, we demonstrate that a Gaussian auto-covariance provides a suitable model for the stochasticity present in typical wind tunnel tests, at least in the case of a Blasius boundary layer. From a physical perspective we demonstrate that it is neither the number of inflection points in a defect, nor the input variance attributed to a defect, that influences the variance in stability characteristics for Poiseuille flow, but the shape/symmetry of the defect. Conversely, we show the symmetry of defects to be less important in the case of the Blasius boundary layer, where we find that defects which increase curvature in the vicinity of the critical point generally reduce stability. In addition, we show that defects which enhance gradients in the outer regions of a boundary layer can excite centre modes with the potential to significantly impact neutral curves. Such effects can lead to the development of an additional lobe at lower wave-numbers, can be related to jet flows, and can significantly reduce the critical Reynolds number.

Neste trabalho utilizamos técnicas de controle e sincronização de sistemas caóticos, visando o uso delas para comunicação com caos. Aplicamos tais técnicas no circuito elétrico de Matsumoto-Chua. Inicialmente, mostramos a sensibilidade dos atratores deste circuito quando variamos os seus parâmetros. Determinamos as suas bacias de atração. Através da análise biespectral, verificamos que o acoplamento quadrático é alto para o atrator tipo Rössler, e quase nulo para o atrator Espiral-Dupla. Para a caracterização global do circuito, apresentamos diagramas, no espaço de parâmetros, com os valores dos expoentes de Lyapunov ou autocorrelação. A seguir estudamos esse circuito com uma perturbação senoidal. Com isto, identificamos novos cenários para a transição para o caos a partir da quase periodicidade. Duas destas transições foram identificados pela primeira vez nesse circuito. Aplicamos ao circuito cinco métodos de controle de caos: supressão de caos por sincronização de freqüências, controle de órbitas periódicas instáveis pelos métodos OGY e de realitnentação , estabilização no ponto ele equilíbrio (método de Hwang), migração e arraste (método OPCL). Finalmente, consideramos dois circuitos de Matsumo-Chua acoplados e determinamos as suas bacias de sincronização. Mostramos que a sincronização dos circuitos acoplados pode não depender das condições iniciais (fronteira das bacias contínua) ou ser extremamente sensível às condições iniciais (fronteira elas bacias elo tipo crivada ou intercrivada). / In this work we use control and synchronization of chaos techniques aiming their implementation in communicating with chaos. These techniques are applied into the electric circuit of Matsumoto-Chua. Initialty, we show the sensibility of the attractors under parameter variations. We determine the attractor basin of attractions. Through the bi-spectral analysis, we verify that the quadratic coupling is high for the Rössler-type attractor, and almost null for the Double-Scroll attractor. For the global charactcrization of this system, we show parameter diagrams of the Lyapunov exponents or auto-correlation. We also study this circuit under a sinusoidal perturbation. In this configuration, we identify new scenario for the transition to chaos through quasi-periodicity. Two of these transitions are identified by us for the first time in this perturbed circuit. We apply five control of chaos techniques: chaos suppression by frequency synchronization, control of unstable periodic orbits by the OGY and feed-back methods, stabilization of the equilibrium points (Hwang method), migration and entrainment (OPCL method). Finally, we consider two acoupled Matsumoto-Chua\'s circuits and determine their synchronization basins. We show that the synchronization in these coupled circuits may not depend on the initial conditions (continuous synchronization basin boundary) or may depend extremely on the initial conditions (riddled or intermingled synchronization basin boundaries).

Investigou-se a gênese de atividade irregular em neurônios de centros geradores de padrões através de modelos eletrofisiologicamente realistas. Para tanto, foram adotadas abordagens paralelas. Primeiramente, desenvolveram-se técnicas para determinar quais os mecanismos biofísicos subjacentes aos processos de codificação de informação nestas células. Também foi proposta uma nova metodologia híbrida (baseada em continuação numérica e em varreduras força bruta) para análise de bancos de dados de modelos neuronais, permitindo estendê-los e revelar instâncias de multiestabilidade entre regimes oscilatórios e quiescentes. Além disto, a fim de determinar a origem de comportamento complexo em modelos neuronais simplificados, empregaram-se métodos geométricos da teoria de sistemas dinâmicos. A partir da análise de mapas unidimensionais perturbados por ruído, foram discutidos possíveis cenários para o surgimento de caos em sistemas dinâmicos aleatórios. Finalmente mostrou-se que, levando em conta o ruído, uma classe de modelos de condutâncias reproduz padrões de disparo observados in vivo. Estas pertubações revelam a riqueza da dinâmica transiente, levando o sistema a visitar um arcabouço determinista complexo preexistente -- sem recorrer a ajustes finos de parâmetros ou a construções ad hoc para induzir comportamento caótico. / We investigated the origin of irregularities in the dynamics of central pattern generator neurons, through analyzing electrophysiologically realistic models. A number of parallel approaches were adopted for that purpose. Initially, we studied information coding processes in these cells and proposed a technique to determine the underlying biophysical mechanisms. We also developed a novel hybrid method (based on numerical continuation and brute force sweeps) to analyze neuronal model databases, extending them and unveiling instances of multistability between oscillatory and resting regimes. Furthermore, in order to determine the origin of irregular dynamics in simplified neuronal models, we employed geometrical methods from the theory of dynamical systems. The analysis of stochastically perturbed maps allowed us to discuss possible scenarios for the generation of chaotic behaviour in random dynamical systems. Finally we showed that, by taking noise into account, a class of conductance based models gives rise to firing patterns akin to the ones observed \\emph{in vivo}. These perturbations unveil the richness of the transient dynamics, inducing the system to populate a preexistent complex deterministic scaffolding -- without resorting to parameter fine-tuning or ad hoc constructions to induce chaotic activity.

A previsão de valores futuros em séries temporais produzidas por sistemas caóticos pode ser aplicada em diversas áreas do conhecimento como Astronomia, Economia, Física, Medicina, Meteorologia e Oceanografia. O método empregado consiste na reconstrução do espaço de fase seguido de um termo de melhoria da previsão. As rotinas utilizadas para a previsão e análise nesta linha de pesquisa fazem parte do pacote TimeS, que apresenta resultados encorajadores nas suas aplicações. O aperfeiçoamento das rotinas computacionais do pacote com vistas à melhoria da acurácia obtida e à redução do tempo computacional é construído a partir da investigação criteriosa da minimização empregada na obtenção do mapa global. As bases matemáticas são estabelecidas e novas rotinas computacionais são criadas. São ampliadas as possibilidades de funções de ajuste que podem incluir termos transcendentais nos componentes dos vetores reconstruídos e também possuir termos lineares ou não lineares nos parâmetros de ajuste. O ganho de eficiência atingido permite a realização de previsões e análises que respondem a perguntas importantes relacionadas ao método de previsão e ampliam a possibilidade de aplicações a séries reais. / The prediction of future values in temporal series produced by chaotic systems can be applied on several fields of knowledge, such as Astronomy, Economics, Physics, Medicine, Meteorology, and Oceanography. The applied method consists on the reconstruction of the phase space, followed by an improvement term of the forecasting. The routines used for the prediction and analysis of this line of research are part of the TimeS package, which presents encouraging results on their applications. The improvement of the computational routines from the package TimeS is built from the thorough investigation of the minimization applied on obtaining the global map and aims for the enhancement of the accuracy and reduction of computational times. The mathematical basis is established and computational tasks are created. The possibilities of adjust functions are amplified, which can include transcendental terms on the rebuilt vectors components and also possess linear or non-linear terms on the adjustment parameters. The improvement allows more accurate predictions and analysis, which answer important questions regarding prediction methods and improve the possibilities of application on real series.

Sinais caóticos são determinísticos, aperiódicos e apresentam dependência sensível às condições iniciais. Esta dependência significa que o estado de dois sistemas caóticos idênticos, iniciados com condições cuja diferença seja arbitrariamente pequena estarão distantes no espaço de fase depois de um tempo finito. Estes sinais podem ser interessantes para algumas áreas da Engenharia de Telecomunicações por apresentarem espectro de Fourier plano, dificuldade de previsão e serem facilmente confundíveis com ruído. Devido à sensibilidade às condições iniciais pode parecer que o sincronismo de dois sistemas caóticos seja impossível. Porém, Pecora e Carroll mostraram que este sincronismo é possível desde que os sistemas obedeçam a certas condições necessárias e suficientes. Este resultado deu um grande impulso para a geração de muitos trabalhos sobre sistemas de comunicação com detecção coerente utilizando sinais caóticos. Regra geral, eles apresentam um subsistema transmissor que gera um sinal caótico a partir do sinal de informação a ser transmitido e um subsistema receptor que consegue produzir um sinal sincronizado com o do transmissor e recuperar o sinal de informação. A literatura mostra que estes sistemas funcionam perfeitamente em condições ideais. O objetivo principal deste trabalho é estudar de forma teórica e numerica o critério de sincronismo de Pecora e Carroll e alguns dos sistemas de comunicação utilizando sinais caóticos propostos na literatura, sobretudo o seu desempenho quando há introdução de ruído branco gaussiano na transmissão e o canal é limitado em freqüência, casos pouco estudados. Mais especificamente, são analisados com certo detalhe os sistemas de comunicação analógica propostos por Cuomo e Oppenheim, por Wu e Chua e o sistema digital Chaotic Phase Shift Keying (CPSK) proposto por Ushio. Mostra-se que nas condições não-ideais citadas, esses sistemas têm desempenho muito pobre no que diz respeito à relação sinal-ruído na saída do receptor. Neste trabalho é apresentada uma solução para este problema no caso de transmissão em canal limitado em banda e é analisada uma proposta de melhoria para o caso de ruído no canal. Conclui-se que, apesar de todas as propriedades interessantes do ponto de vista de comunicações que os sinais caóticos possuem, ainda é necessária muita pesquisa e desenvolvimento para que os sistemas com detecção coerente baseados neles possam concorrer, em situações práticas, com os sistemas em uso atualmente. / Chaotic signals are deterministic, nonperiodic and exhibit sensitive dependence on initial conditions. This dependence means that the states of two identical chaotic systems started with two conditions whose difference is arbitrarily small will be distant in the phase space after a finite time. These signals may be interesting in some Telecommunication Engineering fields because their Fourier spectrum is plane, they are difficult to predict and they are noise-like. Due to the sensitive dependence on initial conditions, it may seem that the synchronism of two chaotic systems is impossible. However, as Pecora and Carroll have shown, this synchronism is possible if the systems satisfy some necessary and sufficient conditions. This result has inspired the development of many communication systems based on coherent detection of chaotic signals. In general, they are composed of a transmitter subsystem that generates a chaotic signal depending on the information to be transmitted and a receptor subsystem that can generate a chaotic signal synchronized with the one on the transmitter and can recover the information signal. These systems are known to work well under ideal conditions. The main objective of this work is to study, theoretically and numerically, Pecora and Carroll's criterion and some of the communication systems using chaotic signals proposed in the literature, specially their behavior when additive white gaussian noise is added to the transmitted signal and the channel is band-limited. Specifically, the analog communication systems proposed by Cuomo and Oppenheim, by Wu and Chua and the Chaotic Phase Shift Keying (CPSK) system proposed by Ushio are analyzed in some detail. We show that when the mentioned non-ideal conditions are present the above systems have poor performance when considering the signal-to-noise ratio at the output of the receiver. In this work a solution is presented for the case of transmission over a bandlimited channel and a method for improving the results in the case of noisy channels is analyzed. We conclude that, regardless all the potential properties chaotic signals may have for communication applications, research and development are still necessary so that systems based on them can surpass in practical situations the usual systems used nowadays.

This dissertation re-examines a particular period of American broadcasting regulation in the 1920s, namely the "chaos" period traditionally labeled as the brief time in between the breakdown of federal radio regulation in early 1926 and the passage of the Radio Act of 1927. Using the ideas of heteroglossia and vernacular discourse drawn respectively from Mikhail Bakhtin and Gerard Hauser, I argue that the media scholarship understanding of chaos needs to be expanded beyond the conventional interpretation of a fatalistic moment which inevitably resulted in the support for broadcast commercialization on a national scale. This theoretical expansion reflects three trends that can be studied in this period: several years of uncertainty in regulatory decision-making, the attempted emergence of a greater variety of stations, and a substantive public debate about the direction of regulation towards commercialization. Chaos can ultimately be looked at as a positive term with ties to the traditional ideal of public interest in broadcasting. I explore three levels and local examples of public discourse to make this argument about chaos, in the process concentrating on Chicago area stations, in particular WCFL and WJAZ, and their experiences during this period. First of all, congressional records of debate over radio regulation as well as the early actions of the Federal Radio Commission establish a level of governmental discourse that struggled to rationalize the elimination of stations towards network commercialization. Second, trade journals such as Radio Broadcast reflect a level of public discourse in close collaboration with regulators, but also reflective of listener voices resistant to the predominance of big commercial stations. Thirdly, WCFL programming, as characterized differently by both Chicago newspaper accounts and station literature, is regarded as contemporary evidence of the heteroglossic and vernacular quality of local broadcasting in urban environments, to be affected negatively by the regulatory turn towards the networks. Re-exploring this period with a more positive evaluation of "chaos," however, can aid scholars in drawing on historical support for media reform movements in an ever-changing communication environment.

ABSTRACT What is visual art making, the artistic creative process, and how does it work? These questions fuelled an investigation at first theoretical, then incorporating an empirical study centered on attaining understanding relating to the elements and dynamics involved in making visual art. The resultant study aims to offer an approach to gaining comprehensive understanding of the artistic creative process, an understanding that may inform art teaching practice, so that art teachers may better understand the related dynamics of their pedagogical processes. Historically the artistic creative process has been accepted as one consisting of different sequential stages of development. This view however, is evolving due to the growing understanding of interrelated dynamics of life processes offered by, for example, neurological studies of the brain. New thinking links earlier philosophical and psychological ideas presented by such thinkers as James (1894) and Dewey (1934), to the work of Baars (1999), Brown (2000), Ellis (1999), Zeki (2000), in offering a deeper understanding of the natural human creative process. The reflective aspect of the artistic creative process is thus related to the way that we process information every minute of our lives; essentially it is the way we progress through life, minute by minute, learning and evolving, affirming self through finding meaning. Study of current theory relating to the processes of the brain inevitably incorporates modern thinking that revolves around dynamic processes. Originating in thermodynamics, Chaos Theory has travelled far from physics to become incorporated into a broad spectrum of disciplines. It offers a common language that relates to the dynamics of human nature, and as such is totally applicable to areas of learning and human interaction. Here used metaphorically, Chaos Theory serves to elucidate interactive aspects of the discipline of art making, with much to offer an understanding of the artistic creative process as it describes exactly the same process of change and growth through experience. A metaphorical use of the language of Chaos Theory provides visual art making with a means of sharing ideas with other academic disciplines that also constantly deal with the dynamics of the human condition, found for example in the close connections between the methods of exploration of both artists and scientists. In studying the phenomenon of ‘scale’ the physicist Feigenbaum commented on the connections between perceptions of artists and those of scientists, pointing to the way in which their perceptions and analysis of things coincide (Gleick, 1987). The visual analysis evident in the work of Turner or Ruskin reflects the same process of detailed conceptual exploration of material collected by the senses as that of a student of any field of scientific exploration. Chaos Theory is important also in that it provides a language accessible by varying levels of expertise, whether at a simple metaphorical or a more sophisticated level. This work charts these dimensions because “The challenge is to reverse the disconnectedness of the present world and to develop a curriculum that is not based on separateness of knowledge from life and being, but upon their inherent unity and integration” (Lovat and Smith, 1995, p.248). / PhD Doctorate

Strategic decision-making is a fundamental process in business management as strategic decisions affect the long-term health of the organisation. However, a constantly and unpredictably changing business environment, becoming progressively more complex as time passes makes strategy formulation increasingly difficult. Shock events such as terrorist attacks, rapidly spreading communicable diseases, and unexpected business failures of large and well-established companies greatly affect organisations by making it difficult to effectively plan for the future. This thesis contributes to the strategic decision-making literature by investigating the role of shock events in a complex system, namely strategic decision-making. Using chaos/complexity theory as an intellectual platform this thesis argues that strategic decision-making is a complex, open, dynamic and non-linear system and that shock events can represent an opportunity in strategic decision-making. A number of contemporary writers are calling for more integrated models. In response this research proposes a generic and integrative framework that highlights the complexity of strategic decision-making and its processes. The research is qualitative and a single-case study approach was chosen, examining the decision-making processes in a large Australian regional airport. Data collection was triangulated, consisting mainly of in-depth interviews with executives but also included questionnaires, and quantitative and qualitative archival data. It was found that shock events influenced strategic decision-making by causing evolutionary changes in the strategic decision-making processes. In addition it was found that shock events impacted on internal drivers such as cognition and organisational culture. The shock event was perceived as an opportunity, which resulted in changing decision-making processes a change in business strategy. It was concluded that environmental perception, intuition and an opportunity-seeking culture can play an important part in strategic decision-making following a shock event.

Sand is an appropriate material to embody and make visible the impulses which may pass through the moving hand and also permeate the universe. Its ability to absorb impressions means it can take on the full range of material states, solid, liquid or vapour, and allows it to speak with the rhythmic language the whole of nature itself uses. Developing a language of forms which more closely speaks this rhythmic language of nature requires an intimate knowledge of the processes of nature. Sand experiments undertaken show the formation a rich array of dazzling patterns. Chaos theory explains this self organizing capacity, and reveals the depth of interdependence of systems within nature. The aspect of self-similarity is also of central significance in appreciating how nature looks and function, and thus how it might be imaged. Drawings from nature were developed using sand as a parameter, starting with the single grain and translating the dynamism of moving sand into mark. Field trips involved looking for waves and repeated lines in nature, and observing how marks form in nature. Chaos theory provides a ground to bring together different spheres of knowledge ?? science, theology and art. It reveals the peculiarities of a material??s behaviour as being of critical importance in the mechanism of evolution. It also provides fresh insight into an incarnational Christian theological perspective, and the relational dynamic within the Trinity. The unity of far and near is also reflected in chaos theory in the self similarity of images. Romantic artists Turner and Van Gogh both engage in the search for a visual language of transcendence through nature using the use of the themes of chaos and order, with an emphasis on physicality and movement. Contemporary artists Goldsworthy, Blanchflower and Kirkeby ground their work in knowledge of material. Changes from solid and rigid to shifting and open show in the development of my work. The immediacy and dynamism of mark making in drawing and staining, ripping and sanding in painting gives process and materiality greater weight. The significance of relationality has reinforced the integrity of horizontal and vertical as expressed in nature and allowed for flexible repositioning of the image within a grid